1. Field of the Invention
The present invention generally relates to vehicle antitheft techniques and, more particularly, to a vehicle antitheft technique using a central authentication device remote from vehicles.
2. Description of the Related Art
There are known various vehicle security systems as a technique to protect a vehicle from theft by preventing an unauthorized engine start or an unauthorized door opening. There is known, for example, a local-type vehicle antitheft system such as an immobilizer system or a smart key system, which performs an authentication between a vehicle and a key of the vehicle. On the other hand, there is also known a central-type vehicle antitheft system, which performs an authentication between a vehicle and a central device remote from the vehicle (for example, refer to Japanese Laid-Open Patent Application No. 2004-143699). The central-type vehicle antitheft system discloses in this patent document performs an authentication according to ID verification through a communication line between a vehicle and a central device and sends a result of the verification by the central device to the vehicle as an authentication response. If the content of the authentication response indicates an agreement or acceptance, an electronic lock is unlocked.
In the local-type vehicle antitheft system, there is a possibility that a theft of a vehicle may be carried out by stealing an ID stored in an electronic key or an antitheft device or canceling the system itself by a certain illegal or unjust method. On the other hand, in the central-type vehicle antitheft system, the state where functions of the vehicle are not permitted to use cannot be cancelled unless an authentication by the central device remote from the vehicle is not approved. Therefore, as compared with the local-type vehicle antitheft system which consists of only vehicle side parts, the central-type vehicle antitheft system can realize a system having higher security.
However, according to the above-mentioned conventional central-type vehicle antitheft system, a time period spent on the authentication is longer than that of the local-type system, and there are many cases in which a user is given a stress by the waiting time. This is because an authentication can be completed within a several tenths of second in the local-type system while it takes an order of second in the central-type local system for the reason of establishing a communication link or the like.
Moreover, in order to prevent a vehicle theft while parking, it is necessary to energize continuously or periodically an in-vehicle communication module, which is capable of communicating with a central device. For this reason, it is possible that the system itself does not work due to running out of a battery caused by an increase in a dark current while parking. Considering the present communication network as a base, an electric current of several hundreds milliampares is needed, which requires an intermittent operation such as once per every 2 seconds. As a result, it further elongates the time until an authentication is completed.
Further, an authentication via a central device cannot be performed at a location where a radio communication with a central device cannot be established (such as an underground parking lot or a mountain-ringed region). This is because the communication network does not cover all areas where a vehicle can move. Additionally, there are locations where connection with a communication network cannot be achieved, such as a hospital or a theme park, in which a jamming (interference) wave is transmitted intentionally so as to protect equipments.